Which type of spark plug leads should be used with a magneto, graphite cored (for RF suppression) or copper cored? Will use of graphite cored HT leads damage a magneto due to the higher lead resistance? My instincts tell me to use copper cored but I am unsure about whether this would be legal to use nowadays due to the electromagetic emissions.

Modern cars tend to use spiral wound HT leads so that they have low resistance compared to graphite but still have good RF suppression. However, I do not know of anywhere that does spiral wound leads in 7mm outside diameter where only the wire can be purchased.

I prefer to stick with the wire leads less chance of them breaking down. I don't think you'll be near enough to cause any interferance if you use them.

Stu.

_________________Engines are just like Pringles .... one is never enough. I used to love tractors all I would ever think/talk about. Then one day out of the blue I went on to statinary engines, So you could say I'm an extractor fan.

I used second hand graphite cored lead on my Petter A1 and worked fine.Put it back to copper cored at the first oportunity though.Got it from a motor cycle shop.As far as legality is concerned, don´t worry. Someone has to complain about it and then they have to track you down and then they tell you to stop using it. Only then will you be prosecuted if you ignore their warning. Plus, modern radios and televisions are not so suscepible to such low frequency radiation.